Radio frequency ablation systems

ABSTRACT

The present invention relates to systems for use for radio frequency ablation. The systems can include one or more of an ablation tool, power source for use with the ablation tool and a backstop for use in conjunction with the ablation tool during surgical procedures. Preferred ablation tools comprise a series of three or more blade-shaped electrodes disposed in a linear, curved, curvilinear or circular array. The backstops are useful for reducing direct physical and thermal heat transfer injuries to the patient or surgeon during procedures using radiofrequency (RF) ablation devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/405,190, filed May 7, 2019, allowed as U.S. Pat. No. 11,291,501,which claims the benefit of U.S. Prov. Appl. 62/811,224 filed on Feb.27, 2019, the entire contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to systems for use for radio frequencyablation.

BACKGROUND OF THE INVENTION

Liver resection is still the management of choice with the best chancefor long-term cure in patients with primary and metastatic hepatictumors. However, only a small percentage of these patients arecandidates for curative surgical resection, because of the tumor size,location near major intrahepatic vessels, multifocality, or inadequatehepatic function related to coexistent cirrhosis. Traditionally, for atumor to be considered appropriate for curative resection, there mustnot be any extrahepatic disease or severe hepatic dysfunction, the tumoror tumors must not be so extensive that too little functioning liverremains after the resection, and at least a 1-cm tumor-free resectionmargin should be attained and there should not be any involvement of theconfluence of the portal vein.

Radio frequency (RF) ablation has become a widely used ablativetechnique for primary and secondary liver tumors and its safety,efficacy, and acceptable local recurrence and short-term survival rateshad been well demonstrated in the literature. RF ablation is a techniquebased on the conversion of electromagnetic energy into heat to destroytumors in various organs. It is either a useful adjunct therapy topartial liver resection or the primary modality of treatment forpatients who were not candidates for curative resection.

Devices for use in RF ablation have been described. See, e.g., U.S. Pat.Nos. 7,367,974 and 10,130,415, both of which are incorporated herein byreference in their entirety. Some of the devices utilize an array ofelectrodes which are inserted into a target organ such as a liver. Thetissue adjacent to the electrodes is coagulated, allowing resection of aportion of the organ. The devices described in U.S. Pat. Nos. 7,367,974and 10,130,415 utilize electrodes which are slidable in the handpiece.Devices such as the Habib 4X are currently in the marketplace. The Habib4X utilizes four needle-shaped electrodes in a square array. Procedureswith this device require multiple insertions and long periods of energydelivery. Additionally, the small diameter needle-like electrodes becomevery hot, which can result in tissue sticking to the electrodes.

Problems with RF devices with slidable electrodes include difficulty ofuse and manufacture. Another problem with RF ablation devices in generalis that energy from the device may cause unintended heating in adjacenttissues or even of a surgeon's hand. Compared with these existingdevices, the devices of the present invention have improved usabilityand can ablate circular, linear, curved or curvilinear regions of atarget tissue in an efficient manner.

SUMMARY OF THE INVENTION

The present invention relates to systems for use for radio frequencyablation. The systems can include one or more components including anablation tool (i.e., an ablation handpiece or just handpiece), powersource for use with the ablation tool and a backstop for use inconjunction with the ablation tool during surgical procedures. Preferredablation tools comprise a series of three or more blade-shapedelectrodes disposed in a linear, curved, curvilinear or circular array.The backstops are useful for reducing direct physical and thermal heattransfer injuries to the patient or surgeon during procedures usingradiofrequency (RF) ablation devices.

In some preferred embodiments, the present invention provides anablation apparatus comprising: a radio frequency (RF) power source; aseries of three or more blade-shaped electrodes that are electricallyconnected to the RF power source, the blade-shaped electrodes eachhaving a tissue-piercing distal end; and an electrically insulatedholder, the three or more blade shaped electrodes non-slidablypositioned (i.e., are in fixed positions) in the electrically insulatedholder wherein the blade-shaped electrodes are oriented so that whenalternating current power is applied via the RF power source to a pairof blade-shaped electrodes a current flows between the adjacentblade-shaped electrodes.

In some preferred embodiments, RF power source applies the alternatingcurrent to a pair or pairs of adjacent blade-shaped electrodes. In somepreferred embodiments, the RF power source applies the alternatingcurrent to a pair or pairs of non-adjacent blade-shaped electrodes. Insome preferred embodiments, the apparatus comprises from between 3 and20 blade-shaped electrodes. In some preferred embodiments, the apparatuscomprises from 3 to 10 blade-shaped electrodes. In some preferredembodiments, the blade-shaped electrodes are positioned in the holder ina linear array. In some preferred embodiments, the blade-shapedelectrodes are positioned in the holder in a circular, oval orelliptical array. In some preferred embodiments, the blade-shapedelectrodes are positioned in the holder in a curved array. In somepreferred embodiments, the blade-shaped electrodes are positioned in theholder in a curvilinear array. In some preferred embodiments, theblade-shaped electrodes are positioned in the holder to form an openarray. In some preferred embodiments, the blade-shaped electrodes arepositioned in the holder to form a closed array.

In some preferred embodiments, the blade-shaped electrodes comprise twoopposing planar surfaces defining a width and planar axis and twoopposing edges defining a thickness and the blade shaped electrodes arecharacterized in having a greater width than thickness. In someembodiments, the blade-shaped electrodes have a rectangular crosssection, while in other embodiments, the blade-shaped electrodes mayhave a diamond-shaped cross section, parallelogram-shaped cross sectionand/or comprise ribs, ridges or similar features. In general, the widthto thickness ratio is greater than 3:1 and can be up to about 10:1 or20:1. In some preferred embodiments, the blade-shaped electrodes arepositioned in the holder so that the planar axes of the blade-shapedelectrodes are substantially parallel to a radial line of a curvedholder. In some preferred embodiments, the blade-shaped electrodes arepositioned in the holder so that the planar axes of the blade-shapedelectrodes are substantially perpendicular to a radial line of a curvedholder. In some preferred embodiments, the blade-shaped electrodes arepositioned in the holder so that the planar axes of the blade-shapedelectrodes are substantially perpendicular to a long axis of a linearholder. In some preferred embodiments, the blade-shaped electrodes areuniformly spaced in the holder. In some preferred embodiments, theblade-shaped electrodes contain depth markings.

In some preferred embodiments, the RF power source comprises asingle-channel RF generator with switching to provide energyindependently to pairs or groups of the blade-shaped electrodes. In somepreferred embodiments, the RF power source comprises a multi-channel RFgenerator with dedicated RF amplifiers for selected pairs or groups ofthe blade-shaped electrodes. In some preferred embodiments, the RF powersource comprises control circuits to control average current flow at theelectrodes according to at least one parameter selected from the groupconsisting of: local temperature of the tissue, local impedance of thetissue, a predetermined current limit, and a predetermined power limit.

In some preferred embodiments, the present invention provides methods oftissue ablation comprising: providing an ablation apparatus as describedabove; inserting the blade-shaped electrodes into a tissue to beablated; applying alternating current via said RF power source so that acurrent flows between designated pairs or groups of electrodes therebycreating a zone of ablated tissue. In some preferred embodiments, thetissue is an organ and the zone of ablated tissue forms a partitionacross the organ and further comprising cutting the tissue of the organat the partition of ablated tissue to reduce blood loss during resectionof the organ. In some preferred embodiments, the partition of ablatedtissue is positioned between the portion of the organ to be resected anda region of blood flow into the tissue. In some preferred embodiments,the organ is a liver.

In some preferred embodiments, the present invention provides ablationapparatus as described above for use in ablating a tissue or resectingan organ. In some preferred embodiments, the tissue is an organ. In somepreferred embodiments, the organ is a liver. In some preferredembodiments, the tissue is tumor tissue. In some preferred embodiments,the tissue is uterine tissue.

In some preferred embodiments, the present invention provides an articlefor use in conjunction with an ablation tool comprising two or moreelectrode units having tissue piercing distal portions, comprising: abackstop formed from an electrically nonconductive material, thebackstop having an upper surface and a lower surface; and a plurality oftissue support structures extending upward from the backstop, the tissuesupport structures spaced to support a target organ above the backstopwhen the article is placed underneath the organ and to receive thetissue piercing distal portions of the two or more electrode units sothat the electrode units pass through and extend beyond the organ andthe tissue piercing distal portions contact the backstop.

In some preferred embodiments, the backstop has a shape selected fromthe group consisting of a planar shape, and rounded shape, a curvedshape, a partial cylindrical shape and a partial spherical shape. Insome preferred embodiments, the tissue support structures have a shapeselected from the group consisting of pillars, ridges, rounded-cones,triangular cones, truncated cones, cylinders, and combinations thereof.In some preferred embodiments, the pillars have a cross-section shapeselected from the group consisting of circular, oval, elliptical, squareand triangular cross-sections. In some preferred embodiments, thebackstop further contains a conductive layer. In some preferredembodiments, the conductive layer is attached to a ground. In somepreferred embodiments, the backstop has a hollow cavity therein toprovide thermal insulation. In some preferred embodiments, the backstophas a rim extending around the perimeter of the backstop to provide abasin for receiving fluid expressed from the organ during ablation.

In some preferred embodiments, the lower surface of the backstopcomprises a plurality of hand support structures extending therefrom toreduce heat transfer from the backstop to the hand of a user. In somepreferred embodiments, the hand support structures are selected from thegroup consisting of pillars, ridges, rounded-cones, triangular cones,truncated cones, cylinders, and combinations thereof. In some preferredembodiments, the pillars have a cross-section shape selected from thegroup consisting of circular, oval, elliptical, square and triangularcross-sections.

In some preferred embodiments, the present invention provides systemsfor use in resection of a target organ comprising: a radio frequency(RF) ablation tool comprising one or more electrode units positioned ina holder having tissue piercing distal portions; and a backstop formedfrom an electrically non-conductive material, the backstop having anupper surface and a lower surface and a plurality of tissue supportstructures extending upward from the upper surface of the backstop, thetissue support structures spaced to support a target organ above thebackstop when the article is placed underneath the organ and to receivethe tissue piercing distal portions of the two or more electrode unitsso that the electrode units pass through and extend beyond the organ andthe tissue piercing distal portions contact the backstop.

In some preferred embodiments, the backstop has a shape selected fromthe group consisting of a planar shape, and rounded shape, a curvedshape, a partial cylindrical shape and a partial spherical shape. Insome preferred embodiments, the tissue support structures have a shapeselected from the group consisting of pillars, ridges, rounded-cones,triangular cones, truncated cones, cylinders, and combinations thereof.In some preferred embodiments, the pillars have a cross-section shapeselected from the group consisting of circular, oval, elliptical, squareand triangular cross-sections. In some preferred embodiments, thebackstop further contains a conductive layer. In some preferredembodiments, the conductive layer is attached to a ground. In somepreferred embodiments, the backstop has a hollow cavity therein toprovide thermal insulation. In some preferred embodiments, the backstophas a rim extending around the perimeter of the backstop to provide abasin for receiving fluid expressed from the organ during ablation.

In some preferred embodiments, the lower surface of the backstopcomprises a plurality of hand support structures extending therefrom toreduce heat transfer from the backstop to the hand of a user. In somepreferred embodiments, the hand support structures are selected from thegroup consisting of pillars, ridges, rounded-cones, triangular cones,truncated cones, cylinders, and combinations thereof. In some preferredembodiments, the pillars have a cross-section shape selected from thegroup consisting of circular, oval, elliptical, square and triangularcross-sections.

In some preferred embodiments, the RF ablation tool is electricallyconnected to an RF power source. In some preferred embodiments, the RFablation tool comprises two or more electrode units and the electrodeunits are oriented so that when alternating current is applied to eitherthe first or second electrode unit, a current flows from that electrodeunit to the other electrode unit. In some preferred embodiments, theelectrode unit is a blade-shaped electrode. In some preferredembodiments, the blade-shaped electrodes are non-slidably positioned(i.e., provided in a fixed position) in the holder. In some preferredembodiments, the apparatus comprises from between 3 and 20 blade-shapedelectrodes. In some preferred embodiments, the apparatus comprises from3 to 10 blade-shaped electrodes. In some preferred embodiments, theblade-shaped electrodes are positioned in the holder in a linear array.In some preferred embodiments, the blade-shaped electrodes arepositioned in the holder in a circular, oval or elliptical array. Insome preferred embodiments, the blade-shaped electrodes are positionedin the holder in a curved array. In some preferred embodiments, theblade-shaped electrodes are positioned in the holder in a linear array.In some preferred embodiments, the blade-shaped electrodes arepositioned in the holder in a curvilinear array. In some preferredembodiments, the blade-shaped electrodes are positioned in the holder toform an open array. In some preferred embodiments, the blade-shapedelectrodes are positioned in the holder to form a closed array.

In some preferred embodiments, the blade-shaped electrodes comprise twoopposing planar surfaces defining a width and planar axis and twoopposing edges defining a thickness and the blade shaped electrodes arecharacterized in having a greater width than thickness. In someembodiments, the blade-shaped electrodes have a rectangular crosssection, while in other embodiments, the blade-shaped electrodes mayhave a diamond-shaped cross section, parallelogram-shaped cross sectionand/or comprise ribs, ridges or similar features. In general, the widthto thickness ratio is greater than 3:1 and can be up to about 10:1 or20:1. In some preferred embodiments, the blade-shaped electrodes arepositioned in the holder so that the planar axes of the blade-shapedelectrodes are substantially parallel to a radial line of a curvedarray. In some preferred embodiments, the blade-shaped electrodes arepositioned in the holder so that the planar axes of the blade-shapedelectrodes are substantially perpendicular. In some preferredembodiments, the blade-shaped electrodes are positioned in the holder sothat the planar axes of the blade-shaped electrodes are substantiallyperpendicular to a long axis of a linear holder. In some preferredembodiments, the blade-shaped electrodes are uniformly spaced in theholder. In some preferred embodiments, the blade-shaped electrodescontain depth markings.

In some preferred embodiments, the RF power source comprises asingle-channel RF generator with switching to provide energyindependently to pairs or groups of the blade-shaped electrodes. In somepreferred embodiments, the RF power source comprises a multi-channel RFgenerator with dedicated RF amplifiers for selected pairs or groups ofthe blade-shaped electrodes. In some preferred embodiments, eachelectrode unit comprises an array of two or more needle shapedelectrodes. In some preferred embodiments, the electrode units arecollapsible. In some preferred embodiments, the ablation tool comprisesfrom 2 to 10 electrode units with needle-shaped electrodes ofcollapsible electrode units. In some preferred embodiments, the RF powersource comprises control circuits to control average current flow at theelectrodes according to at least one parameter selected from the groupconsisting of: local temperature of the tissue, local impedance of thetissue, a predetermined current limit, and a predetermined power limit.

In still further preferred embodiments, the present invention providessystems for use in resection of a target organ comprising: a radiofrequency (RF) power source; a series of three or more blade-shapedelectrodes that are electrically connected to the RF power source, theblade-shaped electrodes each having a tissue-piercing distal end; anelectrically insulated holder, the three or more blade shaped electrodesnon-slidably positioned in the electrically insulated holder, whereinthe blade-shaped electrodes are oriented so that when alternatingcurrent power is applied via the RF power source to a pair ofblade-shaped electrodes a current flows between the adjacentblade-shaped electrodes; and a backstop formed from an electricallynon-conductive material, the backstop having an upper surface and alower surface and a plurality of tissue support structures extendingupward from the upper surface of the backstop, the tissue supportstructures spaced to support a target organ above the backstop when thebackstop is placed underneath the organ and to receive the tissuepiercing distal ends of the three or more blade-shaped electrodespositioned in the electrically insulated holder so that the electrodespass through and extend beyond the organ and the tissue piercing distalportions contact the backstop.

In some preferred embodiments, the from 3 to 10 blade-shaped electrodesare non-slidably positioned in the electrically insulated holder. Insome preferred embodiments, the blade-shaped electrodes are positionedin the holder in an array selected from the group consisting of a lineararray, a curved array, a curvilinear array, a circular array, an ovalarray and an elliptical array. In some preferred embodiments, theblade-shaped electrodes comprise two opposing planar surfaces defining awidth and a planar axis and two opposing edges defining a thickness andthe blade shaped electrodes are characterized in having a greater widththan thickness. In some preferred embodiments, the blade-shapedelectrodes are positioned in the holder so that the planar axes of theblade-shaped electrodes are substantially parallel to a radial line of acurved electrically insulated holder. In some preferred embodiments, theblade-shaped electrodes are positioned in the holder so that the planaraxes of the blade-shaped electrodes are substantially perpendicular to aradial line of a curved electrically insulated holder. In some preferredembodiments, the blade-shaped electrodes are positioned in the holder sothat the planar axes of the blade-shaped electrodes are substantiallyperpendicular to a long axis of a linear electrically insulated holder.In some preferred embodiments, the blade-shaped electrodes are uniformlyspaced in the electrically insulated holder. In some preferredembodiments, the RF power source comprises a multi-channel RF generatorwith dedicated RF amplifiers for selected pairs or groups of theblade-shaped electrodes. In some preferred embodiments, the RF powersource applies the alternating current to a pair or pairs of adjacentblade-shaped electrodes. In some preferred embodiments, the RF powersource applies the alternating current to a pair or pairs ofnon-adjacent blade-shaped electrodes.

In some preferred embodiments, the backstop has a shape selected fromthe group consisting of a planar shape, and rounded shape, a curvedshape, a partial cylindrical shape and a partial spherical shape. Insome preferred embodiments, the tissue support structures have a shapeselected from the group consisting of pillars, ridges, rounded-cones,triangular cones, truncated cones, cylinders, and combinations thereof.In some preferred embodiments, the backstop further contains aconductive layer between the upper and lower surfaces. In some preferredembodiments, the conductive layer is attached to a ground. In somepreferred embodiments, the backstop has a thermal break positionedbetween the upper and lower surfaces. In some preferred embodiments, thethermal break is provided by a hollow cavity positioned between theupper and lower surfaces. In some preferred embodiments, the backstopfurther has a rim extending around the perimeter of the backstop toprovide a basin for receiving fluid expressed from the organ duringablation. In some preferred embodiments, the lower surface of thebackstop comprises a plurality of hand support structures extendingtherefrom to reduce heat transfer from the backstop to the hand of auser. In some preferred embodiments, the hand support structures areselected from the group consisting of pillars, ridges, rounded-cones,triangular cones, truncated cones, cylinders, and combinations thereof.

In some preferred embodiments, the present invention provides methods ofablating a target tissue comprising: contacting the target tissue with abackstop as described above so that the organ is supported on theplurality of upwardly extending tissue support structures, inserting oneor more electrode units of an RF ablation tool into the tissue to definea resection line or area to be ablated, wherein the electrode units havetissue piercing distal portions, so that the electrode units extendthrough the tissue and the tissue piercing distal portions exit theorgan to contact the upper surface of the backstop; and applying RFpower to the electrodes to coagulate tissue along the resection line orin the area to be ablated. In some preferred embodiments, the tissue isan organ. In some preferred embodiments, the tissue is tumor tissue. Insome preferred embodiments, the organ is a liver or uterus. In somepreferred embodiments, the tissue is an organ and the methods furthercomprise resecting the organ along the resection line. In some preferredembodiments, ablation of tissue within the organ creates a partitionpositioned between the portion of the organ to be resected and a regionof blood flow into the tissue.

In some preferred embodiments, the present invention provides a backstopas described above for use to support a tissue for ablation or an organfor resection by an RF ablation tool. In some preferred embodiments, theorgan is a liver or uterus.

In some preferred embodiments, the present invention provides anablation system as described above for use in ablating a tissue orresecting an organ. In some preferred embodiments, the organ is a liveror uterus. In some preferred embodiments, the tissue is tumor tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is perspective view of an RF ablation tool of the presentinvention. FIG. 1B provides a schematic depiction of various bladearrays that may be utilized in an ablation tool of the presentinvention. FIG. 1C provides a schematic depiction of various bladeshapes that may be utilized in ablation tools of the present invention.FIG. 1D provides a schematic depiction of embodiments of the inventionwhere the orientation of the electrodes is varied to allow differentuses of the systems.

FIG. 2 is a cross-sectional view of a tissue separating backstop of thepresent invention with an organ positioned on the backstop andelectrodes from an RF ablation tool extending through the organ.

FIG. 3 is a cross-sectional view of a tissue separating backstop of thepresent invention with a conductive layer and further shown with anorgan positioned on the backstop and electrodes from an RF ablation toolextending through the organ.

FIG. 4 is a cross-sectional view of a tissue separating backstop of thepresent invention with a hollow cavity to provide thermal insulation andfurther shown with an organ positioned on the backstop and electrodesfrom an RF ablation tool extending through the organ.

FIG. 5 is a cross-sectional view of a tissue separating backstop of thepresent invention where the tissue support structures are positioned ina fluid collecting tray feature.

FIG. 6 is a cross-sectional view of a tissue separating backstop of thepresent invention with additional hand support structures on the lowerside and further shown with an organ positioned on the backstop andelectrodes from an RF ablation tool extending through the organ.

FIG. 7 is a block diagram of an RF power supply suitable for use withelectrode arrays of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to systems for use for radio frequencyablation. In preferred embodiments, the present invention providessystems that include one or more of an ablation tool, power source foruse with the ablation tool and a backstop device for use in conjunctionwith the ablation tool during surgical procedures. In some preferredembodiments, the ablation tool comprises a series of three or moreelectrodes disposed in a linear, curved, curvilinear, or circulararrangements or arrays. In some particularly preferred embodiments, theelectrodes are blade-shaped. In still further preferred embodiments, itis contemplated that the backstop devices are useful for reducing directphysical and thermal heat transfer injuries to the patient or surgeonduring procedures using radiofrequency (RF) ablation tools.

RF ablation tools are known in the art. See, e.g., U.S. Pat. No.7,367,974 (incorporated herein by reference in its entirety). RFablation tools can generally comprise a plurality of electrodes and areconnected to a RF source so that electric fields may be generatedbetween the electrodes. The ablation tools and systems provided hereinaddress problems with these previous devices by enhancing usability(e.g., by a surgeon) and efficiency during ablation procedures.

Referring to FIG. 1A, an RF ablation tool 1 is depicted. The RF ablationtool 1 comprises a holder 5 supporting a plurality of elongateelectrodes 10. The elongate electrodes each have a tissue piercingdistal portion 15 such as a sharpened tip 20. In some embodiments, theelectrode is blade-shaped. The holder 5 may be, for example, aninsulating material block having holes cut in the holder 5 to receivemetallic shafts of the elongate electrodes 10 at regular intervals. In apreferred embodiment, the separation of the electrodes 10 is from 0.5 to2.0 cm. The elongate electrodes 10 may be fixed to the holder 10 so asto be moved in unison for rapid insertion. In other words, theelectrodes are fixed in the holder so that they do not slide within theholder. It has been found that even when blade-shaped electrodes areutilized, the electrodes may be inserted into a target organ such as aliver in unison so that an ablation or resection line is defined within(or across) the target organ. This allows ablation of a defined areawith the target organ in a time-efficient manner which addressesproblems associated with devices which utilize sliding electrodes orsmall arrays.

The holder 5 may be any size or dimension suitable for application to atarget organ or region of a target organ. Furthermore, the electrodesmay be provided in a variety of configurations. For example, the holder5 may be from 2 cm to 20 cm along the axis defined by the electrodes. Insome preferred embodiments, the holder can include from 3 to 40, morepreferably from 3 to 20 and most preferably from 3 to 10 electrodes. Insome preferred embodiments, the electrodes are uniformly spaced. Inpreferred embodiments, the electrodes may be provided in a linear,curved, curvilinear, or circular arrangements or arrays. For example,FIG. 1A depicts a linear array of electrodes. In other embodiments, theelectrodes may be arranged within the holder to provide an arrangementcomprising one or more curves.

Embodiments with curved arrays of electrodes can be circular ornon-circular (i.e., the radius of curvature within an array can varyalong the array). The curved arrays can have no inflection point(“C”-shaped), a single inflection point (“S”-shaped), or multipleinflection points. Embodiments with curvilinear arrays can preferablycomprise linear (i.e., straight) section interspersed with one or morecurved sections (“J”-shaped). Furthermore, the curved arrays can be open(“C”-shaped) or closed (“O”-shaped). FIG. 1B provides a schematicdepiction of various blade arrays that may be utilized in an ablationtool of the present invention.

In preferred embodiments, the electrodes are blade-shaped. By“blade-shaped” it is meant that the electrodes have front and backplanar portions and two side edge portions and the planar portions arewider that the edge portions to provide a blade shape. In someembodiments, the planar portions are flat such that the overall blade isflat and has a rectangular cross section. In other embodiments, thefront and back surfaces may be curved, ridged, coined, concave, convex,etc. so that the blade does not have a rectangular cross section. Insome embodiments, the blade-shaped electrodes can contain depthmarkings. FIG. 1C provides a schematic depiction of various blade shapesthat may be utilized in ablation tools of the present invention.

Additionally, as depicted in the schematic diagram of FIG. 1D, in someembodiments the orientation of the electrodes can be varied to allowdifferent uses of the systems. For example, if the electrodes areperpendicular to a radial line of a curved holder, the device can beused to coagulate a volume of tissue within the curvature of the array.Alternatively, if the electrodes are parallel to a radial line of thecurved holder, the device is used to coagulate tissue between adjacentelectrodes.

Holder 5 may be made of a material that is flexible or hinged in one ormore planes in order to allow the user to dynamically change thegeometry of the electrode array, for example, a linear array may be bentslightly in the plane of the large surface of the holder in order toavoid a critical anatomical structure that must remain intact.Additionally, holder 5 may be deformed/hinged out of plane in order toaccommodate the shape of a structure, such as a roughly spherical tumor,which the user desires to treat. In some preferred embodiments, asdescribed in more detail below, the electrodes 10 may be independentlyattached to an RF power source providing independently controllable RFpower to each of the sets of elongate electrodes via cable 25.

The systems of the present invention are not limited to any particularRF ablation tool or electrode set. The ablation tool configurationsdepicted in FIGS. 1A-1D, while being preferred in some embodiments, areexemplary. In other embodiments, the individual electrodes depicted forthe ablation tool in FIG. 1 may be substituted by electrode arrayscomprising two or more needle-shaped electrodes as described in detailin application 62/811,136 which is incorporated herein by reference inits entirety (see also FIG. 8 ). In still other embodiments, theelectrodes may be provided in a collapsible array as also described inapplication 62/811,136.

One of the inherent challenges associated with energy application in thebody is to constrain the energy to the region that the physician wantsto treat in order to leave the surrounding tissues unaffected. Failureto achieve proper energy constraint has resulted in documented cases oflife-threatening damage to surrounding organs.

In order to address these issues, the present invention provides atissue separating backstop that can be used to electrically and/orthermally insulate a tissue or organ to which RF energy is being applied(e.g., a liver) during a surgical procedure (e.g., a resection) toinsulate the organ from adjacent organs or tissues. In some preferredembodiments, the backstop is made from an electrically non-conductivematerial with low thermal conductivity. In some preferred embodiments,the backstop contains a plurality of tissue support structures thatsupport the organ and provide separation from the upper surface of thebackstop, significantly reducing thermal contact between the organ andthe backstop and creating a thermal break. This reduces the RF thermalenergy from heating surrounding tissues (including the surgeon's hand)via thermal conduction and results in faster coagulation of the tissuesbeing treated. Speed is an important factor during liver surgery due tothe highly vascular nature of the liver. During these surgeries, bloodcan be lost at a high rate, so rapid coagulation is essential to limitblood loss which is directly correlated with high rates of morbidity andmortality.

Referring to FIG. 2 , one embodiment of a tissue separating backstop 30of the invention is depicted. The tissue separating backstop 30preferably comprises a base portion 35 having an upper surface 40 fromwhich a plurality of tissue support structures 45 project. In somepreferred embodiments, the base portion 35 is sized to be held by thehand of a surgeon using the device. The tissue support structures 45 arepreferably spaced so that when the tissue-separating backstop is broughtinto contact with organ 50, the organ 50 is supported on the tissuesupport structures and suspended above upper surface 40.

While the embodiments of the tissue separating backstop depicted in theFigures utilize a plate-shaped base portion, it will be understood thatthe base plate (and the backstop as a whole) may be provided in avariety of shapes and that the present invention is not limited toplate-shaped backstops. For example, the base portion can be curved in1-dimension (e.g., a partial cylinder), or in 2-dimensions e.g., (apartial sphere), or in any desired shape. Thus, in addition to a planaror plate shape, the base portion may be curved, or for example, compriserounded or curved portions to allow a comfortable grip of the backstop.As a further example, the base portion may comprise a curved projectionsuitable for grip by the hand of a surgeon.

Furthermore, the embodiments depicted in the Figures utilizepillar-shaped projections for support of the organ above the baseportion. It will be understood that the tissue support structures may bevaried in size and shape. For example, the tissue support structures maybe pillars, ridges, rounded-cones, triangular cones, truncated cones,cylinders, and combinations thereof. In some preferred embodiments, thepillars may have a cross-section shape selected from the groupconsisting of circular, oval, elliptical, square and triangularcross-sections. A benefit of the tissue separating backstop is that itenables uniform application of RF energy through the tissue beingtreated by allowing the distal portions 15 and sharpened tips 20 of theelectrodes 10 to pass completely through the organ 50. The portion ofthe electrodes remaining in the tissue are uniform in thickness and nottapered which contributes to uniform electric fields and thereforeuniform current which is responsible for heating the tissue. It iscontemplated that the choice of tissue support structures allowselectrode arrays of various geometries to pass adjacent to the tissuesupport structures to allow protrusion of the distal portions of theelectrodes beyond the surface of the organ being treated.

As mentioned above, the tissue separating backstop is preferablyconstructed from an insulating material, for example, a biocompatibleplastic. In some embodiments, as depicted in FIG. 3 , the tissueseparating backstop 30 further contains a conductive layer 55 which canoptionally be electrically connected to ground wire 60. Thisconfiguration preferable provides high frequency electrical shielding.

In still further embodiments as depicted in FIG. 4 , a tissue separatingbackstop 30 of the present invention may comprise a cavity 65 in thebase portion 35. It is contemplated that the cavity may provideadditional insulation against transmission of thermal energy. In someembodiments, the cavity 65 may be filled with an insulating gas.

In still other embodiments as depicted in FIG. 5 , the base portion 35of the tissue separating backstop 30 may comprise an indented trayportion 70. In some embodiments, the tissue support structures 45 arelocated in the tray portion 70. It is contemplated that the tray portioncan collect hot liquid that may accumulate during an RF ablationprocedure.

In other preferred embodiments as depicted in FIG. 6 , a tissueseparating backstop 30 of the present invention may further comprise aplurality of hand support structures 75 extending downward from thelower surface 80 of the base portion 35. It is contemplated that thesehand support structures function to further minimize heat transfer fromthe organ 50 being treated to either the surgeon's hand or adjacenttissues. The embodiment depicted FIG. 6 utilize pillar-shapedprojections as an example of hand support structures. It will beunderstood that the hand support structures may be varied in size andshape. For example, the hand support structures may be pillars, ridges,rounded-cones, triangular cones, truncated cones, cylinders, andcombinations thereof. In some preferred embodiments, the pillars mayhave a cross-section shape selected from the group consisting ofcircular, oval, elliptical, square and triangular cross-sections.

The various features of the different embodiments of the tissueseparating backstop described above can be used separately or incombination.

In preferred embodiments, the tissue separating backstops are used inconjunction with an RF ablation system. The RF ablation system may bemonopolar, bipolar or multipolar and may utilize devices comprising 1,2, 3, 4, 5, 6, 7, 8, 9, 10 or more electrodes. FIG. 7 depicts anembodiment from a multipolar device. Referring to FIG. 7 , an ablationtool 1 may be used in conjunction with a power unit 100 providing an RFpower source 105. The power unit 100 provides power to elongateelectrodes 10 (depicted as an array of electrode sets) via anelectronically controllable switching circuit 110 communicating with themultiple conductors 115 of cable 25 (or cables) passing to the elongateelectrodes 10. RF power sources 105 suitable for multiple electrodes aredescribed in U.S. application Ser. No. 10/796,239 filed Mar. 9, 2004 andentitled Multipolar Electrode System for Volumetric Radio FrequencyAblation and U.S. application Ser. No. 10/11,681 filed Jun. 10, 2002 andentitled: Radio-Frequency Ablation System Using Multiple Electrodes,both hereby incorporated by reference in their entirety.

The power unit 100 may also receive signals from each of the elongateelectrode 10 sets from optional thermal sensors (not shown), such as athermocouple or solid-state temperature sensor, attached to the surfaceof the elongate electrodes or within the electrodes. Signals from thesethermal sensors may be received by the power unit at input circuit 120which digitizes and samples the temperature signals and provides them toa microprocessor 125. In a similar fashion, the power unit may receivevoltage and current measurements from each electrode set and providefeedback based on calculated tissue impedance. In still otherembodiments, the amount of power provided to electrode sets ismonitored.

The microprocessor 85 executes a stored program 130 held in a memory 135and also communicates with a front panel control set 140 to provide datato a user and accept user input commands.

While the present invention contemplates that power will be applied tothe sets of elongate electrodes 10 in a bipolar mode as will bedescribed, power unit 100 may alternatively communicate with a groundpad 145 to allow monopolar operation.

The switching circuit 110 provides switches that allow each conductor115 attached to a set of elongate electrodes 10 to be switched to eitherterminal of the RF power source 65 so that the set of elongateelectrodes 10 provides either a return or source of RF power. Switchingcircuit 110 may also be used to disconnect particular ones of theconductors 115 so as to isolate the associated set of elongateelectrodes 10 and to allow a duty cycle modulated control of the powergoing to each set of elongate electrodes 10. Thus, while the powersource 105 may optionally run at a constant rate, control of the powermay be obtained through the switching circuit 110. It is desirable thatswitching of RF circuits occur only at the time that the voltage crosseszero volts. This is commonly known as “zero-crossing”. In preferredembodiments, the switching circuit 110 is connected to themicroprocessor 125 to be controlled thereby. For bipolar operation, eachRF channel has two conductors. The voltage on a single RF conductoroscillates from −V to +V repeatedly. The two conductors from a single RFchannel are out of phase so that when one is at +V, the other is at −V.The switching circuit can be used to supply RF power to multiple pairsof electrodes in sequence from a single channel RF generator, and it canbe used to connect and disconnect the RF power to electrode pairs.

The microprocessor 125 in a preferred embodiment executes the program130 in memory 135 to sequentially control the switches of the switchingcircuit 110 to connect one pair of sets of elongate electrodes 10 to thepower source 110 at each time. Accordingly, at a time period 1, a pairof sets of elongate electrodes will be connected across power source 105for current to flow therebetween. At this time, all other sets ofelongate electrodes 10 are disconnected from the power source 105. At asecond time period 2, a second pair of sets of elongate electrodes 15will be connected across the power source 105 for power to flowtherebetween and a previously utilized set of elongate electrodes isdisconnected from the power source 105. In other embodiments, the powerunits incorporate a separate RF power source for each pair of electrodesso that all volumes of tissue may be energized at the same time. Instill other preferred embodiments, multiple RF power sources areprovided in the power unit and are used to energize pairs of electrodessequentially.

This process repeats itself for the remaining sets of elongateelectrodes 10 until each electrode has been pair-wise connected to thepower source 105. After this, the cycle is reinitiated.

In an alternative embodiment, each of the sets of elongate electrodes 10other than the pair being connected to the power source 105 is connectedto a return path so as to provide an effective virtual ground plane forreturn of current. In monopolar operation, only one set of electrodes isconnected to the RF power source (as opposed to pairs) and the otherconnection of the RF power source is to a ground.

In yet another alternative embodiment, the sequential switching of pairsof sets elongate electrodes 10 does not proceed continuously from leftto right but rather every other sequential pairing is skipped to allowcooling of the tissue near each energized electrode before the nextadjacent pair is energized. Accordingly, a first pair of a set ofelongate electrodes may be connected across the power source 105 andthen a separate second pair, and then a separate third pair, and soforth.

As well as limiting the overheating of tissue, the switching of the setsof elongate electrodes 10 provides other benefits. A large number ofsets of elongate electrodes 10 may create a very low impedance devicewhich may be beyond the current capability of standard power sources105. Accordingly, the switched operation also allows that power to beallocated among pairs of the sets of elongate electrodes 10. Withstandard power sources 105, the ablation region will typically be 1 to 2cm wide and can be obtained in five to ten minutes. The switching amongsets of elongate electrodes 10 may also eliminate shielding effectsamong electrodes providing a more uniform ablation region.

The amount of power deposited at the tissue surrounding each set ofelongate electrodes 10 may be changed by varying the length of theduration for which the sets of elongated electrodes are energized.Alternatively, a high-frequency duty cycle modulation may be imposed onthe power applied across the sets of elongated electrodes according towell-known techniques. The control of power deposited at the tissue neareach set of elongated electrodes 10 may be controlled by thesetechniques according to the temperature measured at each set of elongateelectrodes 10, for example, to reduce power when the temperature risesabove a pre-determined threshold either according to a simplethresholding technique or a more complex feedback loop usingproportional, integral, and derivative terms.

As an alternative to temperature control, the impedance of the tissuebetween each pair of a set of elongated electrodes 10 may be determinedby monitoring the current flow into the tissue and the particularvoltage of the power source 105 (using an in-line current sensor), andthis impedance can be used to control power by decreasing, or shuttingdown power for a certain time period as impedance rises, the latterindicating a heating of the tissue.

Impedance measurements can also be used to gauge the thickness of thetissue being ablated. The tissue may have different thickness in theslice where the electrode array assembly 1 is inserted. By measuringimpedance (with low power application of RF current) between adjacentsets of elongated electrodes 10, the slice thickness along theelectrodes 10 can be estimated before ablating the slice. Power appliedbetween each electrode pair can then be applied according to tissuethickness (e.g. tissue twice as thick requires approximately twice thepower). In one embodiment, this can be achieved by applying a constantvoltage bipolar between each electrode pair. If tissue is twice asthick, impedance is about half as great, and as a result the appliedpower is twice as high with that constant voltage.

Monitoring current and voltage with the microprocessor 125 may also beused to detect excess or low currents to any particular set of elongateelectrodes 10. In the former case, power limiting may be imposed. Thelatter case may indicate a disconnection of one or more sets of elongateelectrodes 10 and an indication of this may be provided on the frontpanel control set 140 to the user.

It will be apparent to those of ordinary skill in the art that a numberof other control feedback techniques may be used including those whichcontrol current flow or voltage or power (the latter being the productof current and voltage) according to each of these terms.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein, but include modifiedforms of those embodiments including portions of the embodiments andcombinations of elements of different embodiments as come within thescope of the following claims.

What is claimed is:
 1. A method of preparing a human liver for resectioncomprising: supporting the liver on a backstop having an upper surfaceand a lower surface and a plurality of tissue support structuresextending upward from the upper surface of the backstop, the tissuesupport structures spaced to support the liver above the upper surfaceof the backstop when the backstop is placed underneath the liver;inserting into the liver a series of three or more blade-shapedelectrodes that are electrically connected to an RF power source, thethree or more blade-shaped electrodes non-slidably positioned in anelectrically insulated holder and having a length so that the electrodesextend through the liver, the three or more blade-shaped electrodesfurther each having a tissue-piercing distal end and wherein the threeor more blade-shaped electrodes in the series each comprise two opposingparallel planar surfaces that extend along the length of theblade-shaped electrodes defining a width and a planar axis and twoopposing edges defining a thickness and each of the three or moreblade-shaped electrodes are characterized in having a greater width thanthickness, and further wherein the tissue support structures are sizedto receive the tissue piercing distal ends of the three or moreblade-shaped electrodes positioned in the electrically insulated holderso that the tissue piercing distal portions of the three or moreblade-shaped electrodes pass through and extend beyond the liver and thetissue piercing distal portions contact the upper surface of thebackstop; applying alternating current via the RF power source to a pairof blade-shaped electrodes within the series of three or moreblade-shaped electrodes in the electrically insulated holder so that acurrent flows between the pair of blade-shaped electrodes and coagulatesthe liver to provide a resection line.
 2. The method of claim 1, furthercomprising resecting the liver along the resection line.
 3. The methodof claim 1, wherein the backstop and the electrically insulated holderare independently positionable.
 4. The method of claim 1, wherein theseries of three or more blade shaped electrodes comprises from three toten blade-shaped electrodes.
 5. The method of claim 1, wherein theseries of three or more blade-shaped electrodes are positioned in theelectrically insulated holder in an array selected from the groupconsisting of a linear array, a curved array, a curvilinear array, acircular array, an oval array and an elliptical array.
 6. The method ofclaim 1, wherein the electrically insulated holder is curved to define aseries of radial lines from the center of the curve and the series ofthree or more blade-shaped electrodes are positioned in the curvedelectrically insulated holder so that the planar axes of theblade-shaped electrodes are parallel to the radial lines of the curvedelectrically insulated holder.
 7. The method of claim 1, wherein theelectrically insulated holder is curved to define a series of radiallines from the center of the curve and the series of three or moreblade-shaped electrodes are positioned in the electrically insulatedholder so that the planar axes of the blade-shaped electrodes areperpendicular to the radial lines of the curved electrically insulatedholder.
 8. The method of claim 1, wherein the electrically insulatedholder is a linear electrically insulated holder having a long axis,wherein the three or more blade shaped electrodes are positioned in theelectrically insulated holder so that the planar axes of theblade-shaped electrodes are perpendicular to the long axis of the linearelectrically insulated holder.
 9. The method of claim 1, wherein thethree or more blade-shaped electrodes in the series are uniformly spacedin the electrically insulated holder.
 10. The method of claim 1, whereinthe RF power source comprises a multi-channel RF generator withdedicated RF amplifiers for selected adjacent pairs of the three or moreblade-shaped electrodes.
 11. The method of claim 10, wherein the RFpower source applies the alternating current to adjacent pairs ofblade-shaped electrodes within the series of three or more blade-shapedelectrodes.
 12. The method of claim 10, wherein the RF power sourceapplies the alternating current to non-adjacent pairs of blade-shapedelectrodes within the series of three or more blade-shaped electrodes.13. The method of claim 1, wherein the backstop has a shape selectedfrom the group consisting of a planar shape, and rounded shape, a curvedshape, a partial cylindrical shape and a partial spherical shape. 14.The method of claim 1, wherein the tissue support structures have ashape selected from the group consisting of pillars, ridges,rounded-cones, triangular cones, truncated cones, cylinders, andcombinations thereof.
 15. The method of claim 1, wherein the backstopfurther contains a conductive layer between the upper and lowersurfaces.
 16. The method of claim 15, wherein the conductive layer isattached to a ground.
 17. The method of claim 1, wherein the backstophas a thermal break positioned between the upper and lower surfaces. 18.The method of claim 1, wherein the electrically insulated holdercomprises a thermal break provided by a hollow cavity positioned betweenthe upper and lower surfaces of the electrically insulated holder. 19.The method of claim 1, wherein the backstop further has a rim extendingaround the perimeter of the backstop to provide a basin for receivingfluid expressed from the organ during ablation.
 20. The method of claim1, wherein the lower surface of the backstop comprises a plurality ofhand support structures extending therefrom to reduce heat transfer fromthe backstop to the hand of a user.
 21. The method of claim 20, whereinthe hand support structures are selected from the group consisting ofpillars, ridges, rounded-cones, triangular cones, truncated cones,cylinders, and combinations thereof.